The use of catalytic alkylation processes to produce branched hydrocarbons having properties that are suitable for use as gasoline blending components is well known in the art. Generally, the alkylation of olefins by saturated hydrocarbons, such as isoparaffins, is accomplished by contacting the reactants with an acid catalyst to form a reaction mixture, settling the mixture to separate the catalyst from the hydrocarbons and further separating the alkylation reactor effluent, for example, by fractionation, to recover the separate product streams. Normally, the alkylation reactor effluent of the alkylation process contains hydrocarbons having five to sixteen carbon atoms per molecule, preferably seven to nine carbon atoms per molecule. In order to have the highest quality gasoline blending stock, it is preferred for the alkylate hydrocarbons formed in the alkylation process to be highly branched and contain seven to nine carbon atoms per molecule.
Recent efforts to improve conventional hydrogen fluoride catalyzed alkylation processes have resulted in the development of new catalyst compositions that contain hydrogen fluoride and a volatility reducing additive. These new catalyst compositions have been found to be quite effective as alkylation catalysts and provide many other favorable benefits.
Regeneration of an alkylation catalyst mixture containing water, HF, acid soluble oil (ASO), and, optionally, a volatility reducing additive generally includes stripping HF from the catalyst mixture using a combination of elevated temperature and isoparaffin or paraffin stripping gas, for inclusion of the stripped HF with the alkylation catalyst mixture. The overhead stream also contains water. The bottoms stream from such a stripper (commonly referred to as a re-run column) contains the ASO and, if present, the volatility reducing additive. Where a volatility reducing additive is used, the re-run column bottoms stream is then separated into an ASO stream and a volatility reducing additive stream, and the volatility reducing additive stream is combined with the alkylation catalyst. Water which enters the unit with the hydrocarbon feed must be removed. Elevated levels of water in the alkylation catalyst can result in increased corrosion of process equipment and alkylate quality degradation. Removal of this water is currently done either by adjusting operation of the stripper to force the water and HF out the bottom with the ASO or if the volatility additive is present, removing a vapor product from the side of the stripping column. Both options involve loss of significant quantities of HF. Therefore, development of an efficient process for removing water from the alkylation process system would be a significant contribution to the art.